Process for the production of polyamide fibres having high linear strength and knot strength

ABSTRACT

PROCESS FOR THE PRODUCTION OF POLYAMIDE FIBRES HAVING LINEAR STRENGTH AND KNOT STRENGTH BY STRETCHING POLYAMIDE MONOFILS AT TEMPERATURES OF 25 TO 35*C. BELOW THE TEMPERATURE LEVEL OF THE CRYSTALLITE MELTING MAXIMUM AT A RATIO OF 1:4.5 TO 1:6.5.

Patented May 4, 1971 US. Cl. 264210 2 Claims ABSTRACT OF THE DISCLOSURE Process for the production of polyamide fibres having linear strength and knot strength by stretching polyamide monofils at temperatures of 25 to 35 C. below the temperature level of the crystallite melting maximum at a ratio of 124.5 to 116.5.

The invention concerns a process for the production of polyamide fibres which have high linear strength and knot strength, in which the monofils obtained by the melt spinning process are stretched at high temperatures.

It is well known that homopolyamides and copolyamides can be spun from spinning apparatus through fine spinning dies to form threads and fibres. It is also known that the mechanical and textile properties of the threads and fibres can be substantially improved by stretching.

In order to obtain the desired optimum properties, this stretching must be carried out at an optimum stretching ratio within a reasonable narrowly limited temperature range. Polyamide fibres may, for example, be spun from a melt extruder through spinning dies into a water bath of to 80 C. and conveyed to a stretching apparatus where they are stretched to a multiple of their original length, so that they are given on an average good linear and knot strength values.

Stretching of polyamide monofils at 30 to 40 C. below the melting point of the polyamides is also known.

It is an object of this invention to provide a process for the production of polyamide fibres which have high linear strength and knot strength which comprises stretching polyamide monofils obtained by the melt spinning process at temperatures of 25 to 35 C. below the temperature level of the crystallite melting maximum of the unstretched polyamide material to an extent of 1:4.5 to 126.5, said stretching being carried out within a contact time of 3 to 10 and preferably 4 to 8 seconds.

Stretching is carried out by passing the polyamide fibres through a heating cupboard which can be heated with continuous temperature variations to 280 C. The temperature level of the crystallite melting maximum of the polyamide is determined by differential thermoanalysis (DTA) with a heating rate of 4 C. per minute.

Differential thermal analysis (DTA) is a dynamic method whereby the phase transitions and chemical transformations that occur during the heating of a polymeric or other material may be detected. In the case of synthetic textile materials the detectable thermal changes include the fusion peaks (crystalline melting maximums). The apparatus used features atmosphere control by diffusion into and out of sample holder cells. A metal sample holder fitted With thermocouples, is suspended in the ceramic core of a standard combustion furnace from a rod attached to a metal plate. With the holder in position, the metal plate rests on the top of the vertically positioned furnace completely covering the opening but the furnace tube remains open at the bottom. Chromel- Alumel thermocouples of 28 gage wire are introduced through the base of the holder and cemented in a fixed position. The EMF representing the temperature difference is amplified by a L & N DC amplifier No. 9835-B. Temperature was measured in the reference substance, calcined alumina (at-A1 0 in a separate well and the rate control thermocouple was located in the outer wall of the sample holder. The signals for the differential temperature and the reference temperature were recorded on time-base chart recorders using two 10 in. single pen recorders (Leeds and Northrup instrument). The rate of heating was controlled by a cam-operated temperature programmer (West Instrument Co.).

The atmosphere is controlled by discharging the desired gas or gases under pressure into the open end of the furnace at flow rates of 3,000 to 6,000 cc./min. via a metal coil gas spreader. Thus, the sample holder is blanketed with the gas and the atmosphere within the same well is achieved by diffusion of gas into the well. The removal of volatile products arising from the thermal degradation of the sample during a run is apparently accomplished by the driving force accompanying volatilization and is also dependent on diffusion.

Under optimum conditions with this apparatus a temperature difference AT of 005 C., which is equivalent to 2 v., could be detected. As previously indicated the reference temperature and not sample temperature was measured so that the temperatures shown on the DTA curves are reference temperatures. Sample temperature is simply determined from the following relationship.

T sample=T ref+AT Fiber, fabric, and some bulk polymer samples of 5 to 50 mg. can be run at heating rates of 1 to 10 C./min. from about 50 to 650 C. Samples are usually prepared by cutting into small squares of in. or in. lengths. The usual method for DTA sample preparation involves grinding or milling to 40-200 mesh. Samples are run in an atmosphere of purified nitrogen to provide nonoxidizing conditions.

The sample packing technique involved the dilution of all samples with the alumina used as the reference material, so that the packing and thermal properties will be determined principally by the reference material regardless of sample shrinkage, melting, decomposition, etc. A modified sandwich packing, developed in previous studies, was used in the present work. About one-third of the reference material to be used is deposited in the sample well as a base layer. The cut pieces of sample are then placed around the thermocouple junction together with reference material and the balance of the reference material constitutes a covering layer.

DTA curves of drawn and undrawn nylon in nitrogen on the gas diffusion apparatus can be prepared. There is a well-defined endothermic peak for polymer fusion indicating the melting point.

The fusion peak for the drawn fiber is much larger and sharper than the undrawn indicating a higher degree of crystallinity and/or orientation, as might be expected.

By polyamide fibres are to be understood polyamide monofils which have a diameter, after stretching of below 1.50 mm.

The improvement in the properties achieved by the process according to the invention can also be determined by the intensity ratios on the X-ray diagram (determination according to Deby-Scherrer with copper-Km radiation).

The monofils stretched by the known processes generally show an intensity ratio of I (002)/I (200) of between 0.10 and 1.00. (002) is the meridianial reflex and (200) the equatorial reflex, which is a measure of the arrangement of the molecular chains within a grid 3 plane. It was found that the products produced by the process of the invention have intensity ratio values of 0.03 to 0.08.

The following table gives the crystallite melting points of polyamides and the stretching temperature.

0.1% solution in m-cresol at 25 C. is spun from a melt spinning extruder into a waterbath through a single aperture or multiaperture spinning die.

The draw-off rate is m./min. and the diameter of the crude fibre is 0.50 mm. The temperature of the crys- The following examples are to further illustrate the invention without limiting it.

EXAMPLE 1 A polycaprolactam of 17, =3.l measured on a 0.1% solution in m-cresol at C. is spun from a melt spinning extruder through a single aperture or multiaperture spinneret into a Water bath. The spun product is drawn off at the rate of 20 m./min. and the diameter of the crude fibre is 0.50 mm. The temperature of the crystallite melting maximum, measured by means of DTA with a heating rate of 4 C./min., of the unstretched fibre is in the region of 233 C. The freshly spun fibre is passed directly from a dressing roller, where it is dressed with an oily preparation, to the heating assembly where it is stretched.

Stretching temperature200 C.

Stretching ratio-l :5 .1

Time of stay in the heating apparatus3.9 sec. Diameter of the stretched fibre0.22 mm.

Linear strength7.22i0.l6 gm./ denier Linear elongation-l5 i2% Knot strength-3.89i0.08 gm./ denier Intensity ratio 1(002) /I(200)0.04

(X-ray intensity measurement using Cu-Ka radiation) For comparison, stretching is carried out at 150 C. Polycaprolactam of 1;, =3.1 is spun and conveyed to the heating apparatus after application of the dressing, as described in Example 1. If the stretching temperature is kept below the temperature level of the crystallite melting maximum of the unstretched material, by more than 35 C. for example, at 170 C., and if the time of stay in the stretching apparatus is less than 3 seconds, the fibre obtained is considerably inferior in its linear strength and knot strength, as can be seen from the following summary:

Stretching temperature-l70 C.

Stretching ratio1:4.8

Time of stay in the heating apparatus1.8 sec. Diameter of the stretched fibre0.23 mm. Linear strength5 .78 $0.13 gm./ denier Linear elongation-21:3

Knot strength3.33 ;0.07 gm./ denier Intensity ratio I(002)/I(200)0.5

EXAMPLE 2 A copolyamide of 85% polyamide 6 and 15% polyamide 11 having a viscosity of =3.l measured on a tallite melting maximum of the unstretched fibre, measured by DTA with a heating rate of 4 C./min., is 218 C. The freshly spun fibre is dressed with an oily dressing and directly conveyed to the stretching apparatus.

Stretching temperaturel85 C.

Stretching ratio1:6.0

Time of stay in the heating apparatus5.5 sec. Diameter of the stretched fibre-0.20 mm. Linear strength-7.781016 gm./denier Linear elongation-17i2% Knot strength--4.56- -0.09 gm./ denier Intensity ratio 1(002) /I(200)-0.06

EXAMPLE 3 A copolyamide of polyamide 6, 10% polyamide 11 and 10% polyamide 12, having a viscosity of 1 =3.2 measured on a 0.1% solution in m-cresol at 25 C. is spun from a melt spinning extruder through a single aperture or multiaperture spinneret into a water bath. The draw-oflf rate is 10 m./min. and the diameter of the crude fibre 0.50 mm. The temperature of the crystallite melting maximum of the unstretched fibre, measured by DTA with a heating rate of 4 C. per min., is 217 C. The freshly spun fibre is dressed with an oily dressing and directly conveyed to the heating apparatus for stretching.

Stretching temperaturel C.

Stretching ratio--1:6.2

Time of stay in the heating apparatus5.2 sec. Diameter of the stretched fibre-0.20 mm. Linear strength-7.22:0.16 gm./ denier Linear elongation-18 i2% Knot strength4.67i0.09 gm./ denier Intensity ratio I(002)/I(200)0.03

What we claim is:

1. A process for the production of polyamide fibers of high linear strength and knot strength which comprises stretching melt-spun polyamide monofils selected from the group consisting of polyamide-6, polyamide-66, polyamide-11, polyamide-l2, copolyamide-6/11, and copolyamide-6/ 11/ 12 at temperatures of 25-35 C. below the temperature level of the crystalline melting maximum as measured by differential thermal analysis with a heating rate of 4 C. per minute of the unstretched polyamide material to an extent in the range of 1:45 to 1:65 said stretching being carried out within a contact time of 3-10 seconds.

2. The process according to claim 1, wherein said stretching is carried out in a heating cupboard.

References Cited UNITED STATES PATENTS 6 FOREIGN PATENTS 648,412 9/1962 Canada 264-290 573,081 11/1954 Great Britain 264-210 5 DONALD J. ARNOLD, Primary Examiner H. MINTZ, Assistant Examiner Robertson 264--290 Hebeler 264-210 Cenzato 264-210 Stow et a1 57---140 264290N Alexander 264-290 10 U8. C1. X.R. 

